In order for 'overthinking' to exist, there'd have to be a 'correct' level of thinking.
Who do you think makes the rules about how much you should 'think' a thing?
The fact is, how much you think about something is a manifestation of who you are. If you think about saving animals from cruelty a lot, that's because you care about the issue. If you think about cooking a lot, it's because you love/hate cooking. You wouldn't try to 'manage' or get an external opinion on whether you were doing it too much; you'd accommodate it. You'd cook more/less. You'd volunteer/get qualified to work for an animal charity.
If his behaviour is upsetting you, respect and accommodate that feeling. If he loves you, he'll respect it too, and it doesn't sound like that's the case, does it?
If someone doesn't respect your feelings, you need to make sure you've explained them clearly, and if that doesn't do the trick, you need to distance yourself from that person. Staying in a situation where someone disrespects you is you disrespecting yourself. Choose situations/people where respect for you (and them) is a given. Put all other relationships to the side.
Your children will benefit far more from the example 'walk away from disrespect' than they will from the example 'put up with disrespect because being respected isn't the most important thing.' They will replicate your example right through their adult life. If you want them to choose 'being respected' as their baseline, then seriously consider not staying in your current situation.
Not easy, especially as he was great before. But holding on to the past and hoping it'll come back is a great way to feel and to be stuck. Value respect of you; pull away from disrespect of you. 